ixgbevf: Set the netdev number of Tx queues

The driver was not setting the number of real Tx queues in the net_device
structure.  This caused some serious issues such as Tx hangs and extremely
poor performance with some usages of the driver.

The issue is best observed by running:

iperf -c <host> -P <n>

Where n is greater than one.  The greater the value of n the more likely
the problem is to show up.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>